Thermionic discharge tube system



THERMIONIC DISCHARGE TUBE SYSTEM Original Filed Aug. 6, 1936 ttorneg Patented July 29, 1941 THERMIONIC DISCHARGE TUBE SYSTEM Henry J. McCarthy, Danvers, Mass, assignor to Hygrade Sylvania Corporation, Salem, Mass, a corporation of Massachusetts Original application August 6, 1936, Serial No. 34,524, now Patent No. 2,122,377, dated June 28, 1938. Divided and this application December 7,1937, Serial No. 178,463

2 Claims. (01. 250-27) This invention relates to wave transmission systems and more especially to such systems as employ thermionic discharge tubes to be operated from a source of alternating heating current.

.An object of the invention is to provide a novel systemof thermionic discharge tube and circiuts whereby the tube can be operated from ordinary A. C. supply lines with a minimum of hum in the output portion of the system.

- A feature of the invention relates to the combination of an improved form of thermionic discharge tube having two separated thermionic cathodes, and special circuit arrangements whereby the cathodes may be heated from a source of alternating current or pulsating current, with a minimum hum.

A further feature relates to the novel organization, arrangement and relative connection of parts which constitute an improved wave repeater, amplifier, oscillator or detector operable from a source of A. C. heating current.

Other features and advantages not specifically enumerated Will be apparent after a consideration of the following detailed descriptions and the appended claims.

While the invention will be described herein as embodied in one particular type of tube, namely a. triode, it will be understood that this is done merely for explanatory purposes, and that the invention can equally well be applied to socalled multi-grid tubes. Accordingly in the drawing, 7

Fig. 1 is a composite schematic structural and circuit diagram showing the invention embodied in a triode.

- Fig. 2 is a view of a tube mount embodying features of the invention.

Fig. 3 is an enlarged detail view of one manner of assembling the bi-part cathode.

Referring to Fig. 1 of the drawing, the numeral l represents any well-known form of en closing envelope either of glass or metal, and preferably although not necessarily, highly evacuated. It will be understood from the ensuing description that the invention can also be embodied in gas or vapor type tubes as well as in vacuum tubes. In accordance with the present invention the electron emitting cathode is coatings to missive temperature, each cathode section is provided with a filament or heater. wire 6, I, and while the drawing shows the heater Wires in the form of a simple V or haire pin shape, it will be understood that this showing is purely schematic and if desired each heater may take the form of a plural folded wire carrying a coating of refractory insulation. As an example of such a heater' reference may be had to U. S. Patent No. 2,158,665. In any event whichever type of heater wire is employed it should be supported within the associated cathode member, so that the wire proper is out of electrical conductive contact with the cathode member.

As shown in the drawing the cathode members and the heater wires .are preferably alike in construction and the right-hand opposing ends of the wires are directly connected by means of a metal straps, while the other opposing ends of the wires are connected by conductors 9 and i0 30 the terminals of the secondary winding H of the usual filament heating transformer. Preferably the electrical midpoint of this secondary winding is connected to ground as shown. 7 Each of the cathode members 2, 3, is also'connected by its respective metal jumper l2, [3 to the conductors 9 and 10. While the tube may be used ingany well-known circuit, merely for purposes of explanation it will be assumed that the tube is to be used as an amplifier of low frequency signals in which eventflthe grid 4 will constitute the control grid and the. signal input circuit represented schematically by a coupling transformer is connected as shown. Thus the secondary winding 12a of the input transformer has one terminal connect-ed to the control grid I 4 and the other end connected to ground, it being understood that, if desired, any of the well known grid biassing arrangements may be employed so as to insure that the tube works on the proper part of its characteristic curve. Likewise the output circuit for the tube may be of any well-known character, and merely for purposes of explanation it is shown as including the primary winding I300 of an output transformer and a source of plate or anode potential form of coupling such as resistancaor choke coupling may be employed.

I have found that with the foregoing described arrangement it is possible to heat the filaments 6 and 1 from a source of low frequency alternating current such for example as that usually supplied by alternating current mains, without the production of appreciable hum in the output circuit. This probably results from the fact thatthe bi-part cathode has both sections arranged symmetrically with respect to the common grid and the common plate, and also from the fact that the sections of the cathode are connected in balanced relation to the alternating current heating circuit, so that the hum components of the heating current in the plateor output circuit, are balanced out. Furthermore this arrangement simplifies the structure of the tube as a whole while achieving the bum elimination, since it is not necessary to bring out separately the leads from the cathode sections and all that is-necessary is to bring out the two leads represented by the conductors 9, Ill, and the grid and plate leads.

While the invention may be embodied in a wide variety of tube structures, there is shown in Fig. 2 one possible arrangement of the various electrodes in the form of a radio tube mount, al-

though it. will be understood that the showing of: Fig. 2 is merely illustrative. In this figure the parts corresponding to similar parts of Fig. 1 are designated by the same numerals. Thus the mount shown comprises a press or other conventionalstandard or header [5 into which are sealed, or upon which are insulatingly supported,.the various lead-in and support wires. IE to 2| inclusive. Thewires l6 and 2| support the tubularplate or anodefi; the wire I! supports the usual, Wire-wound grid 1; while the wires [8 and 20 are connected tothe terminals of: the heater wire 1. The wires I 8 and 20 are likewiseconnected to the terminals of the heater wire. 6. The cathode is formedin two separate sectionsteach comprising a tubular metal sleeve 22, 23 mounted in. longitudinal spaced relation as for example by aninsulating bead or bushing 24 and the outer face of each sleeve being provided with the usual electron emissive coatings 25, 26:. Each heater wire is directly connected by..a. jumper l2, 13 to. its associated cathode sleeve. While the drawing shows the heater wires. 6 and I freely sup-ported within their respective, sleeves, it will be understood that any wellr-knownmanner of insulatingly spacing the wiresfrom their. respective sleeves may be employed, .such for example-as illustrated in U. S.

Patent No. 2,158,665. If desired, thevarious electrodes f-the mount may be held fixed spaced relation by the usual upper and insulator spacer members in the form of mica discs 21, 28. It will be seen therefore that with this arrangement it is possible to connect the heater filaments directly to their associated cathode sleeves within the tube, and it is necessary to bring out only four wires as shown-in Fig. 2, and yet the tube may be used with alternating heating current without the introduction of undesirable hum in the output circuit.

While Fig. 2 shows one possible structure for carrying out the invention, it will be obvious to those skilled in the art that various changes and modifications may be made therein without departing from the spirit and scope of the invention.

This application is a division of application Serial No. 94,524, filed August 6, 1936, Patent No. 2,122,377, dated June 28, 1938.

What I claim is:

1. A wave repeating system including a thermionic discharge tube having a bi-part cathode assembly with a pair of separate emitting members, a heater wire for each member and insulatingly placed therefrom, a direct connection from an end of one heater wire to its associated emitting member, a direct connection from an end of the other heater wire to its associated.

emitting member, the other ends of said heater wires being connected together, an anode common to both said members to receive electron. emission therefrom, a source of heating current connected at its opposite terminals to said members so that said heater wires are in series with said heating current source, a connection from the electrical mid-point of said heating current source to ground, and anoutput circuit including a source of steady potential connected between said anode and ground.

2. A wave repeating-system including a thermionic discharge, tube having a bi-part cathode assembly with a pair of separate emitting members, a heater wire for each member and insulatingly spaced therefrom, a direct connection from an end of one heater, wireto its associated emitting member, a direct connection from an end of the other heater wire to its associated emitting member, the other ends of such heater wires being. connected together, a. grid common to said members, an anode common to said members, a source of heating current connected across said members in series with said heater wires.

and. having its electrical mid-point grounded, an input circuit connected between said grid and said electrical mid-point, and an output circuit connected between said anode and said midpoint. I

, .HENRY' J. MCCARTHY. 

